1. Field of the Invention
This invention relates to syringes and more particularly to a safety syringe having a needle guard for reducing the risk of accidental needle sticks.
2. Background of the Invention
Most syringes used today for medical or laboratory purposes are disposable and are intended to be discarded after a single use. In a standard disposable syringe, a piston or plunger is slidable within a cylindrical fluid chamber, the shank of the piston extending beyond the rear end of the chamber and terminating in a handle. The front end of the chamber has a projecting nozzle that is coaxial with an internally threaded socket adapted to receive a needle supporting hub. When the needle supporting hub is screwed into the socket, the nozzle is then in fluid communication with the needle.
A hypodermic needle and an attached syringe are commonly distributed in sterile condition in a plastic bubble backage to protect them against contamination in storage and shipment. In addition, the hypodermic needle is enclosed in a removable protective cap or overcap whose inlet end snaps onto the needle hub. Thus, after the hypodermic needle and syringe are removed from its package, in order to put it to use one must first remove the protective cap to expose the needle. After the hypodermic needle has been injected into a patient and then withdrawn, before discarding it is preferable to place the protective cap back on the needle hub so that those thereafter handling discarded hypodermic needles for purposes of disposal will not be pricked.
Most accidental needle sticks occur when the needles are being recapped. To recap the needle one must first align the needle with the relatively small diameter inlet of the protective cap. Should the needle be misaligned, as may well happen should the handler be hurried, careless, or distracted, the point of the needle may not enter the protective cap but may instead puncture the finger of the handler.
With the increased awareness concerning the potential for transmission of AIDS and other infectious diseases from used syringes, a number of different devices have been proposed to reduce the risk of accidental needle sticks. One approach to reduce the risk of accidental needle sticks has been to provide a protective shield which is moveable between a retracted and an extended position. A number of different products have been developed to meet the requirement that the needle be permanently covered after the syringe has been used. However, many of these products involve twist-to-lock mechanisms which will often require at least two hands to operate and do not readily indicate when the shield has been locked in the extended position. Other products lock automatically when the shield is extended, however, the locking mechanism remains exposed and may be manually manipulated to retract the shield after the shield has been locked.
Furthermore, many of the products require the user to use both hands to perform complex manipulations of the safety syringe in order to move the protective shield to the extended needle protecting position. Typically, the user must hold the syringe cylinder with one hand while the other hand is used to move the protective shield distally to the extended position. In other products, the user must place their hands unacceptably close the potentially infective needle to move the protective shield to the extended position. It would be preferred for the user to be able to cover the needle by safely using only one hand.